A tool for flanging metal pipes has already been known from, e.g., DE 32 30 444 C2, which tool is intended especially for flanging coated brake pipes of a motor vehicle. This tool, called a flanging press, comprises two parallelepipedic clamping blocks, which have each a plurality of pipe insertion grooves, which are adjusted to certain pipe diameters and are milled to an approximately semicylindrical cross section. These clamping blocks can be braced against each other by means of a screwing device.
Furthermore, a pressing spindle arranged coaxially to a brake pipe clamped between the clamping blocks with replaceable flanging pressure pieces is provided. Furthermore, the sum of the depths of the two pipe insertion grooves belonging together is smaller in this prior-art tool than the pipe diameter of the brake pipe to be flanged.
To make it possible to satisfactorily clamp a brake pipe, especially when it has a plastic coating, as is the case with brake pipes, provisions are made in the prior-art tool for the pipe insertion grooves of the two clamping blocks to have different depths and for at least the deeper pipe insertion groove to be broader than the diameter of the pipe to be clamped. The depth of the pipe insertion groove of one clamping block is greater by about 0.1 mm to 0.4 mm than the radius of the brake pipe to be flanged, while the depth of the other pipe insertion groove of the other clamping block is smaller by at least 0.4 mm than the radius of the brake pipe to be flanged. This design shall lead to asymmetric clamping during the bracing or clamping of the brake pipe in relation to the central axis of the pipe.
It was now found that because of this asymmetric clamping, exact coaxial alignment of the brake pipe to be flanged in relation to the pressing spindle with its replaceable flanging pressure pieces is not guaranteed, especially in the case of brake pipes on which the plastic coating has a greater wall thickness. Furthermore, oval deformation of the brake pipe in question can be frequently observed because of the described dimensions of the individual pipe insertion grooves, as a result of which a male pipe fitting, which is used in brake pipes, is prevented from being able to be pushed over.
On the other hand, as can be determined from the document DE 32 30 444 C2, this shaping is, in turn, essentially necessary in order to make it possible to apply sufficiently strong clamping forces to the brake pipe in the radial direction in order to avoid a displacement in the axial direction during the preparation of the flanged head on the coated brake pipe. In particular, the surface of the plastic coating shall not be damaged. This tool is suitable for brake pipes whose coating is relatively thin. Brake pipes with a greater coating thickness have become known more recently. It was found in these cases that a sufficient, clamping hold of the brake pipes with “thicker” coating can be guaranteed only conditionally by the prior-art flanging press. This is also due, among other things, to the greater dimensional tolerances of the thicker plastic coating and consequently of the actual external diameter of the brake pipe as well as to the greater flexibility of this coating. Even though a snug, clamping hold of the brake pipe in the pipe insertion grooves can be achieved if stronger pressing forces are generated, this leads to a greater deformation of the brake pipe in the area of the flanged head.
Since these deformations develop in the immediate vicinity of the flanged head, precise preparation of such a flanged head conforming to the standards within the preset tolerances is not possible. Thus, on the one hand, this unacceptable permanent deformation of the brake pipe, especially in the area of the flanged head to be prepared, as well as the not exactly coaxial alignment of the brake pipe in relation to the pressing spindle and consequently to the replaceable flanging pressure piece of the pressing spindle during the preparation of a flanged head at the end of the brake pipe always lead to flanged head shapes which are no longer within the tolerance range of a standardized flanged head.